In one prior art of tube retainers, see FIGS. 7 and 8, a shaft is inserted into a sleeve. An outer edge of the sleeve is enclosed by a tube retainer for fixing the shaft in the sleeve. The feature of this prior art is that a buckle is inserted into a hole of the tube retainer. The tube retainer is enclosed in section of the sleeve having a smaller diameter than other portion of the sleeve. Thereby, the shaft can be tightened without sliding down.
Although this structure has the function of tightening a tube, but the tube retainer will over-lock the tube. After being used for a longer time, the stress will concentrate on a tightening portion so that the portion fatigues, as a result the tube deforms, as shown in the FIGS. 7 and 8. FIG. 8 shows the deformation of a receiving space in the tube retainer.
In another prior art, a tube retainer for using in a larger tube is disclosed. The tube retainer includes a sleeve with a tightening ring therein. The tightening ring is engaged within the sleeve and then a tube is tightly enclosed by the tightening ring. The sleeve and the tightening ring are formed with respective openings. Two ends of the opening of the sleeve are formed with respective protrusions protruding outwards. Thereby, studs and nuts can be used to lock the sleeve by passing the stud through the screw holes in the protrusion. However, this structure still concentrate the stress in the openings of the sleeve and the tightening rings. Thus, the defects in the prior art still exist.
Thereby, the prior arts cannot make the stress to distributed uniformly. This is because the space for clamping a tube is not a complete and uniform cycle.